<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box {
            width: 200px;
            height: 100px;
            margin: 200px auto;
        }

        .box input {
            border: 1px solid blueviolet;
            outline: none;
            color: #ccc;
        }
    </style>
</head>

<body>
    <div class="box">
        <input type="text" name="" id="" value="手机" class="te">
    </div>
    <script>
        var input = document.querySelector('input');
        input.onfocus = function () {
            if (input.value == '手机') {
                input.value = '';
                input.style.color = '#000';
                // this.className = this.className + ' 1';
            }
        }
        input.onblur = function () {
            if (input.value == '') {
                input.value = '手机';
                input.style.color = '#ccc';
            }
        }
    </script>
</body>

</html>